The present invention generally relates to an electrical switch for use in high current and high voltage applications. More particularly, certain embodiments of the present invention relate to an electrical switch that reduces arcing when contacts make and break connections.
A wide variety of electrical switches have been proposed for various industrial and commercial applications. Some examples of industrial and commercial applications relate to power tools, electric motors, heating and air conditioning systems, and the like. These varied electrical switches are adapted to operate in high current and/or high voltage applications, as well as with AC and/or DC power supplies.
In general, electrical switches used in high current and high voltage applications include a contact carriage that is moveable within a switch housing. The contact carriage carries contacts that make and break electric connections with associated contacts mounted in the switch housing. FIG. 1 illustrates a top isometric view of a conventional switch housing 10 and a contact carriage 12 removed therefrom. The contact carriage 12 is configured to be moveably mounted within the switch housing 10. The switch housing 10 includes side walls 5, end walls 7 and a bottom 9 that collectively define an interior chamber 11. The switch housing 10 includes contact posts 14 and 15 that are rigidly mounted within the chamber 11 and located proximate front and rear ends 42 and 43, respectively, of the switch housing 10. The contact posts 14 and 15 include faces 16 and 19, respectively, directed toward one another. The bottom 9 of the switch housing 10 is formed with parallel ribs 13 extending between the front and rear ends 42 and 43 of the switch housing 10. A space between the ribs 13 forms a channel 15 that similarly extends between the front and rear ends 42 and 43. The side walls 5 include stepped interior surfaces 3 that are cut by a notch 17 which extends laterally across the interior chamber 11. The notch 17 extends through the ribs 13 and through the channel 15.
The contact carriage 12 includes a body 26 that extends along a longitudinal axis 22. The body 26 includes a front face 21. The contact carriage 12 is configured to be inserted into the chamber 11 of the switch housing 10 with the front face 21 of the contact carriage 12 turned to face the bottom 9 of the switch housing 10. With reference to FIG. 1, before insertion into the switch housing 10, the contact carriage 12 as shown FIG. 1 is rotated 180 degrees about the longitudinal axis 22 until the front face 21 of the contact carriage 12 faces the bottom 9 of the switch housing 10.
The body 26 of the contact carriage 12 includes support posts 28 and 34 formed on the front face 21 proximate opposite ends of the body 26. A pair of C-shaped supports 30 and 32 are also provided on the front face 21 of the body 26 and arranged to face in opposite directions along the longitudinal axis 22. The C-shaped supports 30 and 32 are positioned near corresponding support posts 28 and 34. The support post 28 and the C-shaped support 30 are separated by a gap that receives a contact bridge 18. The support post 34 and C-shaped support 32 are separated by a gap that receives contact bridge 20. Contact bridges 18 and 20 are oriented parallel to one another and transverse to the longitudinal axis 22. The C-shaped supports 30 and 32 receive springs 36 and 37, respectively, that bias contact bridges 18 and 20, respectively, outward against support posts 28 and 34. The contact bridges 18 and 20 include contact pads 24 and 25, respectively, facing outward in opposite directions. The contact bridges 18 and 20 are permitted to move along the longitudinal axis 22 within a limited range of motion.
The support posts 28 and 34 include tip portions 29 and 35, respectively, extending upward away from the front face 21. When the contact carriage 12 is loaded into the chamber 11, the contact tips 29 and 35 are turned down to rest in, and slide along, the channel 15 formed between the ribs 13. Hence, ribs 13 and tip portions 29 and 35 cooperate to control the direction of motion of the contact carriage 12 with respect to the switch housing 10 during operation. Once the contact carriage 12 is loaded into the chamber 11, the contact bridges 18 and 20 are aligned with contact posts 14 and 15, respectively, such that pads 24 on contact bridge 18 align with faces 16 on contact posts 14. Similarly, pads 25 on contact bridge 20 align with faces 19 on contact posts 15. As the contact carriage 12 is slid in the direction of arrow A, pads 24 engage faces 16 to form an electrical connection through contact bridge 18 and between contact posts 14. When the contact carriage 12 is slid in the direction of arrow B, pads 25 engage faces 19 to afford an electrical connection through contact bridge 20 between contact posts 15. Only one of contact bridges 18 and 20 is electrically connected with the corresponding contact posts 14 and 15, respectively, at any single point in time. Hence, when contact bridge 18 engages contact posts 14, contact bridge 20 is disengaged from contact posts 15, and vice versa.
FIG. 2 illustrates a partial end isometric view of the contact carriage 12 to better illustrate a dielectric hood 46 mounted on the body 26. The dielectric hood 46 is configured to reduce arcing by separating the contact bridge 20 from the contact posts 15 when the contact carriage 12 is moved in the direction of arrow A. The dielectric hood 46 includes a central beam 48 located above, and extending parallel to, the contact bridge 20. Opposite ends 47 of the central beam 48 are held within notch 17 (FIG. 1) in the stepped interior surfaces 3 of the side walls 5. The central beam 48 is slidably mounted to legs 49 provided on the body 26. The notch 17 holds the central beam 48 at a fixed position in the chamber 11. Hence, when the contact carriage 12 moves within chamber 11, the dielectric hood 46 moves relative to the body 26.
A pair of isolation flaps 50 and 52 are mounted on opposite ends of the central beam 48 proximate the pads 25 (shown in dashed lines in FIG. 2) on opposite ends of the contact bridge 20. The isolation flaps 50 and 52 are curved in an L-shape as shown in FIG. 2 to extend forwardly from the central beam 48 and to curve downward toward the body 26. When the central beam 48 is moved in the direction of arrow C with respect to the body 26, the central beam 48 rotates in the direction of arrow D until the isolation flaps 50 and 52 cover the pads 25 on the front of the contact bridge 28. When the central beam 48 is moved in the direction of arrow E with respect to the body 26, the central beam 48 is rotated in the direction of arrow F, causing the isolation flaps 50 and 52 to pivot upward to expose the pads 25 on the contact bridge 20. FIG. 1 illustrates the dielectric hood 46 moved to a position at which the contact bridge 20 and the pads 25 are entirely exposed to faces 19 on the contact posts 15.
Returning to FIG. 1, when the contact carriage 12 is loaded into the switch housing 10, opposite ends 47 of the central beam 48 are received within the notch 17. As the contact carriage 12 is moved in the direction of arrow A, the notch 17 holds the central beam 48 in a fixed position relative to the switch housing 10, thereby causing the relative motion between the dielectric hood 46 and the body 26 of the contact carriage 12 in the direction of arrow C (FIG. 2) which in turn causes the central beam 48 to rotate in the direction of arrow D to cover pads 25 on the contact bridge 20 with the isolation flaps 50 and 52. In reverse, when the contact carriage 12 is moved in the direction of arrow B (FIG. 1), the notches 17 continue to retain the central beam 48 at a fixed location relative to the switch housing 10. As the contact carriage 12 is moved in the direction of arrow B, the body 26 and dielectric hood 46 experience relative motion therebetween in the direction of arrow E which in turn causes the central beam 48 to rotate in the direction of arrow F. Rotating the central beam 48 in the direction of arrow F moves the isolation 50 and 52 upward away from the contact bridge 20 to expose the pads 25 to the faces 19.
The foregoing conventional structure provides a high current and/or high voltage switching mechanism.
However, conventional switches, such as the switch shown in FIGS. 1 and 2, have met with limited success. In particular, conventional electrical switches continue to experience an unduly large amount of arcing in high current and/or high voltage applications. There remains a tendency for arcing to occur during making and breaking of connections between the contact pads 24 and 25 and faces 16 and 17 on contact posts 14 and 15, respectively. Each time an arc occurs, a carbon residue is left on the faces 16 and 17 of the contact posts 14 and 15 and upon the contact pads 24 and 25. In addition, each time an arc occurs, the risk exists that small divots may be burned or chipped into the faces 16 and 17 and/or contact pads 24 and 25. Carbon buildup and divots create a rough interface between the contact pads 24 and 25 and faces 16 and 17. As this interface becomes more uneven and as more carbon builds up, the electrical switch exhibits higher internal resistance which causes the switch to heat up during operation. Undue heating of the electrical switch may damage the switch and detract from its useful life.
A need remains for an improved electrical switch that reduces carbon buildup and surface divots at the contact interface, in order to extend the overall operating life and current/voltage carrying capacity of the electrical switch.
An electrical switch is provided that includes a housing having at least one contact retention chamber formed therein. The housing includes an opening through one wall of the contact retention chamber through which an actuator extends. A contact assembly is movably mounted within the contact retention chamber of the housing. The contact assembly includes contacts that are movable along an arcuate path aligned at an angle to a longitudinal axis of the housing. The actuator includes an insulated over-molded portion that retains a conductive member therein. The conductive member is configured to engage the contacts. The housing slidably retains the actuator to permit movement of the actuator and the conductive member along the longitudinal axis of the housing. The actuator drives the contacts along the arcuate path between engaged and disengaged positions with the conductive member as the actuator moves along the longitudinal axis of the housing drives.
Optionally, the contact assembly may include first and second sets of contacts that are configured such that the first set of contacts is normally open, while the second set of contacts is closed when the switch is an OFF position. When either set of contacts is closed, it engages opposite sides of the conductive member to convey power through the conductive member between the closed set of contacts.
Optionally, the housing may include first and second contact retention chambers separated by an insulated divider. The insulated divider includes an opening therethrough that slidably receives the conductive member. The conductive member moves back and forth through the divider between the first and second contact chambers to engage one of the first and second sets of contacts. When the conductive member is located in the first contact chamber, the contacts in the second contact chamber are open and electrically isolated from one another by an intervening dielectric member, and vice versa.
The actuator may include one or more grooves cut in its exterior and aligned with corresponding elbows bent into the bodies of the contacts. The grooves and elbows cooperate to bias the contacts outward away from the actuator along the arcuate path as the actuator is slidably moved along the longitudinal axis of the housing. The contacts travel along the arcuate path at a first instantaneous rate of movement and the actuator moves along the longitudinal axis of the housing at a different second instantaneous rate of movement. By using different first and second instantaneous rates, the actuator increases the rate at which the contacts are moved toward and away from the conductive member with respect to the rate at which the actuator is moved along the housing.